# 递归
def method1(n):
    if n == 1 or n == 2:
        return 1
    else:
        return method1(n - 1) + method1(n - 2)


# 迭代
def method2(n):
    if n == 1 or n == 2:
        return 1
    f1, f2 = 1, 1
    for i in range(3, n + 1, 1):
        f1, f2 = f2, f2 + f1
    return f2


if __name__ == '__main__':
    n = int(input())
    out1 = method1(n)
    print(out1)
